Author
Topic: Picking a Voltage Regulator IC (Read 4844 times)

I need some help on picking the right type of voltage regulator. And I also have a quick question on its implementation as a replacement as a MOSFET, youll see what I am talking about. Basically I need to convert an input of +3V DC to an output +5V DC .8 - 1Amp ; however because the VccIn will be comming from a PIC output I do not know if I should instead grab the VccIn from the my 18V DC 1.5 Amp powersupply, in which case there would be two distributions of voltages, 12V with most of the amps going to a mator and 5V with mA's going to a relay. If i can run off of the PIC OUTPUT could I do away with a MOSFET for switching voltages? I am pretty sure i am making this WAY to compliacted, i am pretty sure all i need is some ENHANCED MOSFETS and some big resistors to creat different voltages instead of going beyound my electrical abilities and setting up a V-Reg IC.

Ok I am not entirely sure what you mean, but maybe I can help you some . . .

PIC's will output 5V DC, but can only supply a few mA. If you want to power anything from a PIC above a few mA, you need a circuit that can handle the current. You probably want to amplify the voltage too. A MOSFET, a relay, a motor driver IC, or a power op-amp can do this. It really depends on what you want to do, what you have, and how much time/money you want to spend towards it.

Also, try to avoid resistors at all costs if you are dealing with high current applications - they waste a ton of energy as dissipated heat.

A voltage regulator (a tutorial I have been meaning to write for a long time now) is really only useful if your circuit cannot tolerate voltage fluctuations. They are very inefficient and waste a lot of energy, so avoid them if you can.

If a voltage regulator is what you need but you are still dealing with high power stuff, consider a switching voltage regulator (go to www.dimensionengineering.com for one that I use). They are much more expensive, but also much more efficient and works with a selectable voltage.

Yeah I agree with you that it is too much to hassle with using voltage regulators. So I am just going to stick with the MOSFETs, I got some MOSFET N-ENHANCED IRF510s' in the mail last week, I've been meaning to play with them but didn't have the time, that's why I thought the SPICE sim would work (but you know as well as me they are just a little screwy at times). You got my main point that I wanted to switch voltages, but it is my fault my post was way too disorganized. What I really meant to say hope this makes sense My circuit has an incomming voltage of around 26V DC from the a wall transformer. What I need to do is split this IN LINE into 3 other voltages, 1st line 5V (for PIC) , 2nd line 6V (For MOSFET: Drain to Source to Relay) and 15V (This is for the DC Motor controller that uses the same power as the motor which is quite large and needs probobly around 1.5 Amps). I feel like I should be paying you guys for this lol, sadly I am a Bio major and don't have time to take electronics courses. Anyways could you perhaps give me some ideas as how to go about this? perhaps three really simple 3 pin v-regs (heat an issue).

Dimension Engineering has some REALLY fancy stuff I wouldnt mind getting my hands on, maybe when i make some real $$ though, if that ever happens, LOL

for the PIC you want to use a voltage regulator. make sure the regulator can handle a 26V input, some cant. they just have three pins, one for your 26V, one for ground, and one for your output 5V. really simple.

for the other two you would want to use mosfets. make sure they have built in 'fly back diodes.' its kinda complicated, but basically it prevents your mosfets from frying when recieving current going the wrong way (very common with motors). you also might want to use op-amps to amplify the voltage going into the gate of your mosfet (high gate voltage means lower internal resistance meaning higher efficiency therefore less heat to melt itself). you will probably see the diodes (if they are built in) in the datasheet of the mosfet.

however the mosfet will only turn on and off your relay and motor, and not actually control the voltage. i highly recommend finding a lower voltage source. RC battery packs maybe? otherwise, you will need a switching regulator and it still wont be pretty.

nothin wrong with a bio major making circuits, heck im a mechanical engineer

WoW! That post was great! answerd all of my questions. My relays will be controlling only the reverse (DPDT) and the ON-OFF (SPST) of my DC Motor controller which uses a NE556 timer (rated at 16V) to control the speed of the motor. So I am sure it wont be a problem, I could just insert a fuse. The controller can also use seperate sources for motor and the ne556 so I don't think i will have any problems. I really appreciatied your help today.BTW: You went to CMU and graduated recently? It's such a big university but you didn't by chance know anyone named Guideon N. he was a physics major and graduated ~3 yrs ago

Just know that a fuse wont neccessarily protect your circuit components from damage. All they do is turn off your circuit when its drawing waaaay too much current, such as an unexpected short. Your circuit components are still likely to be destroyed before the fuse blows, but at least there wont be a fire or massive meltdown or electrocute yourself . . .

If a motor rated at 16V gets 26V, it is likely to overheat and the coils will melt together, destroying the motor. Going over just a few volts is generally OK.

Check the spec sheet of the NE556 what the highest voltage it can take is. Most electronics IC's I am aware of dont handle above 20V too well.